Electrodynamic loud-speaker



June 24, 1947.

J. F. MARQUIS ET AL ELECTRODYNAMIG LOUD-SPEAKER Filed Nm). s, 1944Patented June 24, 1947 UNITED STATES PATENT OFFICE Charles, Ill.,Aassignors ing Co., St. Charles, Iii

to Operadio Manufactura corporation of Illinois application November 3,1944, serial' No. 561,776 4 Claims. (C1. 17a-1155) This inventionrelates to an acoustic transducer,l 'commonly termed a loud speaker, andemployed as an element of a radio receiver or of a public addresssystem.

n object of the invention is to provide new and improved acoustictransducer, together with an expeditious method of assembling the same,

Another object of the invention is to reduce the overall depth, ascompared 4with that of the conventional acoustic transducer in which themagnetic motor is mounted behind the diaphragm.-

Itis also an object ofthe invention to provide a transducer having itsmagnetic motor assembly disposed in front of the diaphragm withoutrequiring any supporting braces or Webs for said motor at the forwardside of the diaphragm;

A further object of the invention is the reduc tion of manufacturingcost by the elimination of .the conventional 'arms and other partsusually required for supporting the magneticY motor in front of thediaphragm.

More specifically, the invention provides a suhst'antial frame orhousing disposed behind the diaphragms'together with means for rigidlysup` porting the permanent magnet or electromagneticmotor from thecentral portion of this house ing, the diaphragm being provided with acentral aperture through which a supporting connection extends to carrythe motor at a position in front of the diaphragm.

Other objects and advantages of the invention will appear fromthefollowing description taken in connection with the drawings in which,

Fig. 1 is a substantially axial-sectional View of a transducer or loudspeaker embodying; this in vention and provided type O'f motor-l Fig. 2is av sectional; view similar to Fig. l., but with portions broken`away; showing an electromagnetic motor mounted in accordance with theprinciples of the invention.

Fig. 3 is aV front view or elevation o'f the vstructure shown in Fig; 1.

Fig. 4 is an axial sectional view showing step in the assembly process.for centering the opening'in the diaphragm and positioning thev voicecoil in accordance with a definite standard.

Fig. 5 is a fragmentary axial section taken substantially at the sameplane as Figs. 1v and 2, showing a modified securing means for themagnet ic motor- 4 Fig;..6 is a fragmentary sectional view similar toFig, 5, showing another modification 'of the se curing means.

with a permanent magnet Fig. 7 is also a fragmentary sectionalviewsimilar to Fig. 5, showing a further modification.

While the invention is susceptible of various modifications andalternative constructions, the embodiments shown in the drawing anddescribed hereinafter are by way of illustration only, and it is notintended that the invention be limited thereto or thereby, but .that allmodifications and alternative constructions falling within the scope ofthe invention be included herein as defined by the claims.

In Fig. 1, the supporting housing is shown at I, being of frusto-conicalform and terminating in an outer flange 2 to which the periphery of theconical diaphragm 3 is adhesively attached. The central portion of thehousing l is a flat circular wall Il reinforced by a disk 5 which may beof somewhat heavier stock than the remainder of the housing I to addrigidity to the back wall 4, and which is secured theretov by anyconventional method such as welding or riveting.

The diaphragm 3 is formed with a central opening surrounded by a shortintegral collar or ilange 3a, and a centering member in the form of acrimped or corrugated flexible diaphragm, is adhesively secured to thiscollar 3a, the peripheral portion 5a of the centering member beingsecured to a shoulder Ia of the housing I. Said housing I may be, andfrequently is, made with substantial cut-out areas, giving it the natureof a spider rather than an enclosing housing, and when thus constructedis sometimes termed basket; but, if preferred, the conical wall of thepart I may be continuous, and for the purpose of this invention it isimmaterial which design is employed for this part.

In the central opening of the diaphragm 3 there is secured a tubularsupport 'l which may be of paper or other non-magnetic material havingits upper end adhesively fastened to the inner surface of the collar 3aof the diaphragm and carrying at its lower end the voice coil 8 whichacts as the armature of the magnetic motor by which the diaphragm 3 isvibrated. Terminals or lead wires for the coil 8 are not shown inthefdravving, but it will be understood that such wires extend from theVc'oil to the radio receiver orl telephone system into which the speakeror transducer is connected.

Fig. 11 shows a permanentA magnet I0 which is preferably of the alloytypecomposed of the material known as A-lnico V or other suitablemagnetic material and' a central polepiece II extends coeaxially fromthe magnet IIJ, being secured theretonby a screw I2. Thescrew also holdsin place the back plate I3 which carries the cylindrical member I4 ofthe magnetic motor, said member acting as the opposite pole of themagnet and providing an annular air gap I5 in which the voice coil 8 issupported with operating clearance. The magnet Il and the part I4 arerigidly secured to the reinforced back wall 4, 5 of the housing I bymeans of a clamping bolt or screw I6 extending through the centralopening in said back wall and through an annular spacer member I1 ofnonmagnetic material which is interposed between the back wall and thecenter pole II. Prefei ably, the end of the part II is reduced in diamneter to t accurately within a recess in the mating end of the spacer I1,while said spacer is tted into a central opening in the back wall 4which does not extend through the reinforcing member 5, but thusprovides a centering recess in which the spacer I1 may be fitted andclamped by means of the screw I6. Preferably, the screw is provided witha locking washer I8 disposed between its head and the part 5.

The structure shown in Fig. 2 is substantially identical with that shownin Fig. 1 except that instead of the permanent magnet Ii), the motorincludes an electromagnet having an inductor coil 20, and the centralpole 2I extends throughout the depth of this coil and is shown with areduced portion 22 which is riveted over the end plate I3 by which theouter pole I4 is carried. The remaining parts being similar to thoseshown in Fig. l, they are designated by corresponding referencenumerals.

As indicated in Figs. 1 and 3, the flange 2 of the supporting housingterminates in an annular flange portion 2a which serves to center andconfine the edge of the diaphragm 3 and a mounting gasket or cushionring 23 which is adhesively fastened to this marginal part of thediaphragm in position to contact the face of a baille or panel on whichthe speaker may be mounted by bolts or screws passing through the parts2, 3 and 23. In previous devices of this character in which the magneticmotor was mounted in front of the diaphragm adjacent its concave side,the motor was supported by radially extending arms or webs attached tothe outer flange 2 of the housing and usually to secure a smooth andfinished appearance it was necessary to notch or interrupt the gasket 23to accommodate the ends of these arms. With the present structure, suchsupporting arms are eliminated and the additional work on the gasket 23,together with the labor of securing the supporting arms in position, isavoided.

To simplify the assembly and to insure not only that the magnetic motorwill be properly centered and fitted within the voice coil, but alsothat it will be interchangeable with a re placement motor, if required,the special jig, shown in Fig. 4, may be employed in tting the diaphragmand voice coil into the housing. The voice coil 8 and its supportingcylinder 'I are fitted onto a plug 3B and the diaphragm and centeringmember 6 are then glued to the part 1 in their correct relativepositions. The plug 3U includes a reduced portion 3I which fits into thecentral recess bf the' back wall 4, while a reduced threaded portion 32extends through the central opening in the part 5 so that a wing nut 33may be applied to clamp the plug 3i) in position during the periodrequired for drying the glue which holds the parts 3, 6 and 1 together.As soon as the plug 30 has been inserted in the back wall the peripheralportion 6a of the centering member 6 may be glued in position on theshoulder I8L and the outer edge of the diaphragm 3 may be adhesivelysecured, if desired, in the cupped flange 2 of the housing, and may beclamped therein with the gasket 23 in position. At the end of the dryingperiod the plug 30 is removed, thus leaving the central opening in thediaphragm 3 accurately positioned with respect to the central openingsin the back wall 4, 5 so that when a magnetic motor is installed it willbe properly centered with respect to the diaphragm and the voice coil 8.

Fig. 5 shows a modified construction in which a spacer 40 is substitutedfor the spacer I1 and is formed with a conically tapered portion 4Intting into a conical recess 42 in the plate 5x attached to the backwall 4. The bolt 43 thus draws the spacer 40 and the attached centerpole 2| (or II) snugly into position, the end of the tapered portion 4Ibeing made slightly underflush with respect to the outer surface of theplate 5X to insure that it will be drawn tightly into the conical socket42 by the screw 43. Preferably, a relatively large clamp washer 44 isdisposed under the head of the screw 43 to distribute the clampingpressure, and the lock washer 45 is included to hold the parts inadjusted position.

In the arrangement shown in Fig. 6 the nonmagnetic scaper 50 is fittedto the end of the center pole 2| (or l I) in the same manner asheretofore described, but the outer end of the spacer is threaded at 5Ito engage corresponding threads in the plate 5y secured to the back wall4. A lock nut 52 is then screwed onto the protruding threads 5I of thespacer. The screw 53 acts independently of these parts to perform thesingle function of securing the spacer 50 to the center pole 2|, and alock washer 54 is provided to prevent loosening of this connection inoperation.

Fig. 7 shows a further modication in which the non-magnetic spacer 60 onthe pole 2| (or I I) includes a reduced portion 6I which ts snugly in acentral opening in the plate 5 secured to the back 4. This reducedpartion 6I is slightly underflush with respect to the outer face of theplate 5c to insure being drawn snugly into position by the clamp screw62 which operates against a clamping washer 63 and is provided with alock washer 64 directly under its head.

It will be seen that with any of the structures herein described, orwith modications involving the same principles, the magnetic motor willbe firmly and rigidly supported at the front side of the diaphragm so asto occupy space within the cavity of the diaphragm, thus providing avery compact structure as compared with transducers in which the motoris mounted behind the diaphragm; but that this arrangement does notrequire the use of supporting arms extending radially from the magneticmotor to the rim of the housing and thus projecting in front of thediaphragm and more or less impairing the propagation of sound therefrom.It will also be evident that with the standardized positioning of thecen-v tral opening in the diaphragm and in the voice coil which isrendered possible by use of the assembly plug herein described, anyproperly constructed motor may be fitted accurately into place so as tofunction efficiently with this assembly, and if repair or replacement ofthe motor should become necessary it can be readily removed andremounted or replaced with equal accuracy and with a minimum of time andskill.

It will be understood that if the supporting housing is made of magneticmaterial, such as steel, the spacer Il, (or 40, 50 or 6D) will bepreferably formed of non-magnetic material, such as brass oraluminum,and in that case the screw l1 (or 43, 53 or 62) should also be ofnon-magnetic material. If the housing itself is non-magnetic, the otherparts may be madeof steel, although it will still be preferable to haveythem of non-magnetic metal so that the polar flux will tend to beconcentrated in the vicinity of the voice coil.

We claim as our invention:

1. A loud speaker comprising a rigid unitary supporting housing havingthe general outline of the frustum of a cone, said housing having a wallat the small end and having accurately finished supporting means at saidwall, a sub-assembly comprising a voice coil support, speaker diaphragmand cylindrical Voice coil, said speaker diaphragm being of the conicaltype with the small end joined to said voice coil, means for securingthe large end of said speaker diaphragm to the large end of saidhousing, means for securing said Voice coil support to the housing in anaccurate position with respect to the finished supporting means of saidhousing Wall to accurately pre-position said voice coil, a two-piecefield structure comprising an axial pole piece and annular pole piece,said two pole pieces having accurately nished surfaces dening an annularair gap adjacent one end of said aXial pole piece, means for rigidlysupporting said annular pole piece solely from said axial pole piece atthe other end of said axial pole piece, said axial pole piece having theone end thereof accurately nished to cooperate with the finishedsupporting means at said housing wall and means for rigidly supportingsaid axial pole piece at said one end only from said housing Wall, saidfield structure being adapted to be symmetrically disposed within thespace enclosed by said housing with the accurately finished housing partand axial pole end cooperating to provide an, inverted dynamic speakerassembled in preadjusted centered relation.

2. The structure of claim 1 wherein said means for maintaining saidfield structure against said housing comprises readily removable lockingmeans accessible from the outside of the small end of the housing.

3. The structure of claim 1 wherein said housing is shaped to provide anannular ange adjacent to and symmetrical with said wall and wherein saidVoice coil support is secured to said flange.

4. The structure of claim 1 wherein said housing is shaped to provide anannular flange adjacent to and symmetrical with said wall and whereinsaid voice coil support is a solid annular member having the outer endsecured to said flange with said housing forming an enclosed air chamberbetween said voice coil support and housing end wall.

JOHN F. MARQUIS. CARLETON T. WEIBLER.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,808,297 Dempster June 2, 19321,820,585 Tolerton Aug. 25, 1931 1,886,816 Jensen Nov. 8, 1932 2,186,576Cornwell Jan. 9, 1940 1,941,476 Jensen Jan. 2, 1934 1,941,477 JensenJan. 2, 1934 1,952,357 Blumlein et al Mar. 27, 1934 1,970,038 Bowier etal Aug. 14, 1934

